1. Field of the Invention
This invention relates to a magnetic component for an electric machine such as a motor. In particular, an amorphous metal component such as a rotor or stator for a high efficiency radial-flux electric motor is described. The term xe2x80x9celectric motor,xe2x80x9d as used herein, refers generically to a variety of rotating electrical machines which additionally may include electric generators as well as regenerative motors that may be operated optionally as electric generators.
2. Description of the Prior Art
A radial-flux design electric motor typically contains a generally cylindrical stator made from a plurality of stacked laminations of non-oriented electrical steel. Most commonly, each lamination has the annular shape of a circular washer along with xe2x80x9cteethxe2x80x9d that form the poles of the stator. The teeth protrude from the inner diameter of the stacked laminations and point toward the center of the cylindrical stator. Each lamination is typically formed by stamping, punching or cutting mechanically soft, non-oriented electrical steel into the desired shape. The formed laminations are then stacked and bound to form a stator. During operation the stator is periodically magnetized with ensuing losses due to magnetic hysteresis, reducing the overall motor efficiency.
Although amorphous metals offer superior magnetic performance when compared to non-oriented electrical steels, they have long been considered unsuitable for use in electric motors due to certain physical properties and the corresponding fabricating limitations. For example, amorphous metals are thinner and harder than non-oriented steel. Consequently, conventional cutting and stamping processes cause fabrication tools and dies to wear more rapidly. The resulting increase in the tooling and manufacturing costs makes fabricating amorphous metal components such as rotors and stators using such techniques commercially impractical. The thinness of amorphous metals also translates into an increased number of laminations in the assembled component, further increasing its total cost.
Amorphous metal is typically supplied in a thin continuous ribbon having a uniform ribbon width. However, amorphous metal is a very hard material making it very difficult to cut or form easily, and once annealed to achieve peak magnetic properties, becomes very brittle. This makes it difficult and expensive to use conventional approaches to construct amorphous metal magnetic components. The brittleness of amorphous metal also causes concern for the durability of a motor or generator which utilizes amorphous metal magnetic components. Magnetic stators are subject to extremely high magnetic forces which change at very high frequencies. These magnetic forces are capable of placing considerable stresses on the stator material which may damage an amorphous metal magnetic stator. Rotors are further subjected to mechanical forces due both to normal rotation and to rotational acceleration when the machine is energized or de-energized and when the loading changes, perhaps abruptly.
Another problem with amorphous metal magnetic components is that the magnetic permeability of amorphous metal material is reduced when it is subjected to physical stresses. This reduced permeability may be considerable depending upon the intensity of the stresses on the amorphous metal material. As an amorphous metal magnetic stator is subjected to stresses, the efficiency at which the core directs or focuses magnetic flux is reduced resulting in higher magnetic losses, reduced efficiency, increased heat production, and reduced power. This phenomenon is referred to as magnetostriction and may be caused by stresses resulting from magnetic forces during the operation of the motor or generator, mechanical stresses resulting from mechanical clamping or otherwise fixing the magnetic stator in place, or internal stresses caused by the thermal expansion and/or expansion due to magnetic saturation of the amorphous metal material.
Non-conventional approaches to amorphous metal component designs have been proposed. In one approach, a xe2x80x9ctoothlessxe2x80x9d stator, consisting simply of a tape-wound amorphous metal toroid, has been suggested. While this approach is attractive for manufacture, the geometry is not favorable magnetically. The flux path results in excess eddy current losses and the large air gap between the stator and rotor limits the performance and control of the motor. A second approach attempts to replicate the conventional stator shape by combining a tape-wound amorphous metal toroid with stacks of cut amorphous metal. The wound amorphous metal toroid forms the back-iron of the stator and the cut amorphous metal stacks are mounted on the inner diameter of the toroid to form the teeth or poles. While this approach reduces the air gap between the stator and rotor, the magnetic flux must cross the many layers of tape wound back-iron as the flux passes from the tooth to the back-iron. This greatly increases the reluctance of the magnetic circuit and the electric current required to operate the motor.
A third approach, disclosed by U.S. Pat. No. 4,197,146 to Frischmann, fabricates the stator from molded and compacted amorphous metal flake. Although this method permits fabrication of complex stator shapes, the structure contains numerous air gaps between the discreet flake particles of amorphous metal. Such a structure greatly increases the reluctance of the magnetic circuit and the electric current required to operate the motor.
A fourth approach, taught by German Patents DE 28 05 435 and DE 28 05 438, divides the stator into wound pieces and pole pieces. A non-magnetic material is inserted into the joints between the wound pieces and pole pieces, increasing the gap, and thus increasing the reluctance of the magnetic circuit and the electric current required to operate the motor. The layers of material that comprise the pole pieces are oriented with their planes perpendicular to the planes of the layers in the wound back iron pieces. This configuration further increases the reluctance of the stator, because contiguous layers of the wound pieces and of the pole pieces meet only at points, not along full line segments, at the joints between their respective faces. In addition, this approach teaches that the laminations in the wound pieces are attached to one another by welding. The use of heat intensive processes, such as welding, to attach amorphous metal laminations will recrystallize the amorphous metal at and around the joint. Even small sections of recrystallized amorphous metal will increase the magnetic losses in the stator.
A fifth approach, disclosed by U.S. Pat. No. 4,255,684 to Mischler, involves fabricating the stator from either laminated strips of amorphous metal or from moldable composites of amorphous metal flake. Stator fabrication using laminated strips involves bending the strips to the desired stator shape. The mechanical stresses imparted on the laminated strips during the shaping operation will increase the core loss of the finished stator. This approach does not envision annealing of the stator to relieve the mechanical stresses. Stators fabricated from moldable composites of amorphous metal flake will contain numerous air gaps between the discreet flake particles. This will greatly increase the reluctance of the magnetic circuit and the electric current required to operate the motor.
Notwithstanding the advances represented by the above disclosures, there remains a need in the art for improved amorphous metal motor components. This is so because these components are essential for improving the efficiency of motors.
The present invention provides an amorphous metal magnetic component for a high efficiency radial-flux electric motor. The component may be a rotor or stator. In one embodiment the component comprises a plurality of substantially similarly shaped layers of amorphous metal strips laminated together. Each layer may be generally annular and may further comprise a plurality of tooth sections or poles protruding radially from the annular section and integral therewith. The layers are adhered in registry to the adjacent layers by mechanical or adhesive means. The layers are preferably electrically insulated from one another to reduce eddy current losses.
The present invention further provides a bulk amorphous metal magnetic motor component which exhibits very low core loss under periodic excitation. As a result, the magnetic component is operable at frequencies ranging from DC to as much as 20,000 Hz. It exhibits improved performance characteristics when compared to conventional silicon-steel magnetic components operated over the same frequency range. The component""s operability at high frequency allows it to be used in fabricating motors that operate at higher speeds and with higher efficiencies than possible using conventional components. A magnetic component constructed in accordance with the present invention and excited at an excitation frequency xe2x80x9cfxe2x80x9d to a peak induction level xe2x80x9cBmaxxe2x80x9d may have a core loss at room temperature less than xe2x80x9cLxe2x80x9d wherein L is given by the formula L=0.0074f(Bmax)1.3+0.000282f1.5(Bmax)2.4, the core loss, the excitation frequency and the peak induction level being measured in watts per kilogram, hertz, and teslas, respectively. The magnetic component may have (i) a core-loss of less than or approximately equal to 1 watt-per-kilogram of amorphous metal material when operated at a frequency of approximately 60 Hz and at a flux density of approximately 1.4 Tesla (T); (ii) a core-loss of less than or approximately equal to 12 watts-per-kilogram of amorphous metal material when operated at a frequency of approximately 1000 Hz and at a flux density of approximately 1.0 T; or (iii) a core-loss of less than or approximately equal to 70 watt-per-kilogram of amorphous metal material when operated at a frequency of approximately 20,000 Hz and at a flux density of approximately 0.30 T.
The bulk amorphous metal magnetic component of the present invention can be manufactured using numerous ferromagnetic amorphous metal alloys. Generally stated, these alloys are defined by the formula: M70-85 Y5-20 Z0-20, subscripts in atom percent, where xe2x80x9cMxe2x80x9d is at least one of Fe, Ni and Co, xe2x80x9cYxe2x80x9d is at least one of B, C and P, and xe2x80x9cZxe2x80x9d is at least one of Si, Al and Ge; with the proviso that (i) up to ten (10) atom percent of component xe2x80x9cMxe2x80x9d can be replaced with at least one of the metallic species Ti, V, Cr, Mn, Cu, Zr, Nb, Mo, Ta, Hf, Ag, Au, Pd, Pt, and W, (ii) up to ten (10) atom percent of components (Y+Z) can be replaced by at least one of the non-metallic species In, Sn, Sb and Pb, and (iii) up to about one (1) atom percent of the components (M+Y+Z) can be incidental impurities.
The present invention also provides methods of constructing a bulk amorphous metal motor component. An implementation includes the steps of stamping laminations of the requisite shape from ferromagnetic amorphous metal strip feedstock, stacking the laminations in registry to form a three-dimensional object, applying and activating adhesive means to adhere the laminations to each other and give the component sufficient mechanical integrity, and finishing the component. The finishing step may include one or more of removing any excess adhesive from the component, giving it a suitable surface finish, and giving it final component dimensions. The method may further comprise one or more optional heat-treating steps to modify the mechanical properties of the amorphous metal feedstock to facilitate punching or to improve the magnetic properties of the component These steps may be carried out in a variety of orders and using a variety of techniques including those set forth hereinbelow.
The present invention is also directed to a bulk amorphous metal component constructed in accordance with the above-described methods. In particular, a bulk amorphous metal magnetic motor component constructed in accordance with the present invention is suited for use as a stator in a high efficiency, radial flux, permanent magnet, DC electric machine.
The present invention further provides a brushless radial-flux DC motor having an amorphous metal stator comprising a plurality of generally annular layers of amorphous metal strips configured to form a generally cylindrical stator. Each layer may further comprise a plurality of tooth-shaped pole sections protruding radially from the generally annular region and integral therewith. The teeth may be directed radially inward in a conventional motor design or outward for use in an inside-out or cup design motor. The motor also comprises a rotor having at least one permanently magnetized section with at least one pair of oppositely directed magnetic poles and bearing means for rotatably supporting the stator and rotor in a predetermined position relative to each other.
The advantages afforded by the present invention include simplified manufacturing, reduced manufacturing time, reduced stresses (e.g., magnetostrictive) encountered during construction of bulk amorphous metal components, and optimized performance of the finished amorphous metal magnetic component.